Musical teaching and tuning apparatus

ABSTRACT

A crystal-controlled oscillator is utilized in conjunction with a digital frequency divider chain, which divider chain is provided with means for selecting any one of a plurality of division ratios, to derive a selected tone within the tempered scale. The output signal from the divider chain, which is a square wave, is passed through a selected voicing network to provide the approximate timbre of a musical instrument. The amplified signal from the voicing network drives a transducer such as a set of head phones or a loudspeaker. A decibel meter is provided to monitor the intensity of sound issuing from the transducer such that hearing tests across the important part of the frequency spectrum can be readily carried out. Additionally, in order to assist in ear training a pupil and also to achieve means for determining very closely the pitch of an instrument being tuned or otherwise compared against the crystal-controlled standard, a counter chain is used with logic circuits in such a manner that the difference in period between a crystal-controlled tone and a tone of unknown, but moderately close to very close frequency is measured over every other half cycle for subsequent display on a zero center meter which deflects in one direction to indicate a sharp unknown tone and in the other direction to indicate a flat unknown tone, there being no deflection if the periods of the known and unknown tones are sufficiently close. For interval training a student may be presented with a first precise tone, derived through the divider chain, against which he attempts to adjust a variable frequency oscillator to arrive at an interval indicated on a switch controlling the counter chain. However, that switch adjusts the counter chain in such a manner that it measures a period corresponding to the tone the student is seeking rather than that derived through the frequency divider chain. Thus, the meter display provides an accurate indication as to whether he is sharp or flat with respect to the tone he is seeking.

United States Patent Barnum 1 1 Apr. 22, 1975 1 1 MUSICAL TEACHING ANDTUNING APPARATUS {76] Inventor: Phillip R. Barnum, 8031 East Willetta,Mesa, Ariz. 85207 [22] Filed: Sept. 18. 1973 [21] Appl. No.: 398,443

Related US. Application Data [63] Continuation-impart of Scr. No.255.674. May 22.

1972. abandoned.

[52] US. Cl. 84/454; 84/470; 84/DIG. 18; 324/79 D [51] Int. Cl. GlOg7/02; G09b 15/00 [58] Field of Search "84/101. 1.03. 1.09-1.11. 84/119.1.27, 454. 470, 477. DIG. 18; 324/79 R, 79 D [56] References CitedUNITED STATES PATENTS 2.901.699 8/1959 Motz ct a1 84/454 X 3.470.78510/1969 Shallenberger et a1. 84/470 3.472.116 10/1969 Schott 84/4543.509.454 4/1970 Gosscl.... 324/79 R 3.541.915 11/1970 Rhodes 84/4703.631.756 1/1972 MacKworth-Young 84/454 3.722.352 3/1973 lhrke et a1.84/454 3,722.353 3/1973 Wcsthaver 84/454 1766.818 10/1973 Prohofsky84/454 3.774.494 11/1973 Reid. Sr. et a1.. 84/470 3.782.237 1/1974Okamoto 84/470 3.795.169 3/1974 Bclcher..... 84/454 3.817.144 6/1974Okamoto 84/470 [57] ABSTRACT A crystal-controlled oscillator is utilizedin conjunction with a digital frequency divider chain. which dividerchain is provided with means for selecting any one of a plurality ofdivision ratios, to derive a selected tone within the tempered scale.The output signal from the divider chain. which is a square wave, ispassed through a selected voicing network to provide the approximatetimbre of a musical instrument. The amplified signal from the voicingnetwork drives a transducer such as a set of head phones or aloudspeaker. A decibel meter is provided to monitor the intensity ofsound issuing from the transducer such that hearing tests across theimportant part of the frequency spectrum can be readily carried out.Additionally. in order to assist in ear training a pupil and also toachieve means for determining very closely the pitch of an instrumentbeing tuned or otherwise compared against the crystal-controlledstandard, a counter chain is used with logic circuits in such a mannerthat the difference in period between a crystalcontrolled tone and atone of unknown, but moderately close to very close frequency ismeasured over every other half cycle for subsequent display on a zerocenter meter which deflects in one direction to indicate a sharp unknowntone and in the other direction to indicate a flat unknown tone. therebeing no deflection if the periods of the known and unknown tones aresufficiently close. For interval training a student may be presentedwith a first precise tone. derived through the divider chain. againstwhich he attempts to adjust a variable frequency oscillator to arrive atan interval indicated on a switch controlling the counter chain.However. that switch adjusts the counter chain in such a manner that itmeasures a period corresponding to the tone the student is seekingrather than that derived through the frequency divider chain. Thus. themeter display provides an accurate indication as to whether he is sharpor flat with respect to the tone he is seeking.

4 Claims, 5 Drawing Figures ammo" coumnoa MLIFIEI 21 f 2: 1 mm cram"EXTERNAL MP0! "I? F LYEI PATENTEDAPRZZHTS SHKU 3 BF 5 lllllllllll WM QJT QQUW MUSICAL TEACHING AND TUNING APPARATUS This application is aeontinuation-in-part of my copending application Serial No. 255.674.filed May 22. I972. entitled "Musical Teaching and Tuning Apparatus",and now abandoned.

This invention relates to the musical arts. and more particularly. toelectronic apparatus for providing ear training as well as means forachieving very accurate tuning and hearing sensitivity tests.

Many devices are known in the prior art which purport to issue a more orless accurately tuned pitch against which a musician. craftsman, orstudent can compare his efforts by ear. Other devices provide a visualindication of differences between a master tone represented in someanalog and a tone generated in one manner or another by the operator.For example, the well known pitch pipe. when activated like a harmonica.produces a tone which may be a standard frequency. by way of example,for a particular string on a guitar or violin. The drawback to this typeof tuning is that the accuracy achieved is completely determined by thetuners ear with a complicating factor in that the timbre of the sound isdifferent from the timbre of the instrument being tuned. Another deviceused for tuning guitars comprises six resonant reeds tuned to the sixfrequencies to which the six guitar strings should be tuned. To use thisdevice. a string is plucked and tuned until the corresponding resonantreed is observed to vibrate with maximum excursion. However. excursiontravel is also dependent on the magnitude of the blow that activates thestring. and it is very difficult to determine when maximum excursion isachieved.

Among the more advanced tuning devices is the socalled strobe tunerwhich utilizes a motor-driven set of discs rotating at a closelycontrolled speed. Vibrations from the instrument being tuned are pickedup by a microphone and amplified to cause light amplitude fluctuationsat a corresponding rate behind the discs which are circumferentiallydivided into alternating opaque and translucent areas. When the unknowntone is in tune, a selected area along the radius ofthe disc will appearto stand still in accordance with the well-known stroboscopic effect.This apparatus, while useful. has certain distinct drawbacks andlimitations. For tuning string instruments, the intensity of the stringmovement [which is, of course, damped) determines the intensity of thelights such that one must be very adept at making a quick observation.Another problem in utilizing this apparatus in tuning plucked stringinstruments is that the pitch of the plucked string does not immediatelysettle down when the string is first plucked or struck. and thetransient deviations are variable according to the specific place andmethod the string is activated. From a teaching standpoint, there is noaudio involvement to enhance ear accuracy; i.e.. the apparatus is notintended as a teaching aid but rather as a working tool. It is possible,of course. to use laboratory grade electronic equipment such as afrequency counter to measure the frequency of an unknown sound to a highdegree of accuracy. However. those skilled in the electronics art willappreciate that the necessity for additional interface equipment coupledwith the expense and complexity of such frequency counters renders suchan approach completely impractical for ordinary tuning purposes.

As previously noted, the above-described prior art devices. which areonly representative, are primarily concerned with providing a tool withwhich an experienced musician or craftsman can tune an instrument. Noneof the known prior art devices provide means by which an unskilledperson can compare his tuning efforts against a master tone to a veryfine degree of accuracy. whether for the purpose of tuning or eartraining.

Thus. it is a broad object of my invention to provide improved apparatusfor facilitating tuning and musical ear training.

It is another object of my invention to provide such apparatus whichprovides an unmistakable visual indication of the qualitative differencebetween a preselected, accurate tone, and a tone of unknown fre quencyproduced by the efforts of the operator.

It is still another object of my invention to provide such apparatuswhich indicates the interval difference between an accurately generatedtone and a tone generated under control of an operator which should beat a predetermined interval.

It is still a further object of my invention to provide apparatus whichpermits the foregoing comparisions at all intervals including theoctave. across a range ofseveral octaves.

It is yet another object of my invention to permit such comparisons tobe made in the timbre of the different instruments to create familiaritywith the characteristic sounds of such instruments.

In yet another aspect. it is an object of my invention. by virtue of theaccurate pitch and sound level control inherent therein. to provideapparatus for readily carry ing out standardized hearing tests acrossthe most important portion of the audio spectrum.

Yet another object of my invention is to provide such apparatus which isreliable, simple to use, and relatively inexpensive to produce.

The subject matter of the invention is particularly pointed out anddistinctly claimed in the concluding portion of the specification. Theinvention. however. both as to organization and method of operation, maybest be understood by reference to the following description taken inconnection with the accompanying drawings, of which:

FIG. 1 is a block diagram ofa presently preferred embodiment of theinvention.

FIG. 2 is a schematic representation of the electrical components andcircuitry utilized in the emobodiment of the crystal oscillator 1,frequency divider chain 2. and tone selector switch 3.

FIG. 3 is a schematic representation of the electrical components andcircuitry utilized in the embodiment of the period gate logic l2,counter and decoder 13 and period selector switch 14.

FIG. 4 is a schematic representation of the electrical components andcircuitry utilized in the embodiment of the isolation amplifer 24 andperiod (count) comparator 18.

FIG. 5 is a schematic representation of the electrical components andcircuitry utilized in the embodiment of the squaring circuit and filternetwork 23.

Referring now to FlG. I, it will be observed that a crystal oscillator1, having a nominal frequency of 3.87l87l mhz for reasons which will beset forth below. drives a frequency divider chain 2 which has a divisionratio under control of a tone selection switch 3.

Frequency divider chain 2 is preferably of the digital. integratedcircuit type which has become widely available in recent years. Thoseskilled in the art will appreciate that different division ratios arereadily achieved by variously interconnecting the adjacent stages andfeedback between nonadjacent stages of the divider chain according towell known techniques. The presently preferred electrical embodiment ofcrystal oscillator 1. frequency divider chain 2 and tone selector switch3 is depicted in FIG. 2. Frequency selection is the function of the toneselector switch 3 which is pref erably calibrated in indicia indicatingboth the frequency output of the divider chain 2 and the correspondingnote on the tempered scale. Thus. if the switch is preset to theposition 440-A" the interconnections between the stages and thefrequency divider 2 will afford a division ratio of 8800 whereby theactual output frequency from the divider will be 439.99. The other tonesof the tempered scales may be derived with similar accuracy by varyingthe division ratio of the frequency divider chain 2, and has been foundthat the previously indicated crystal frequency of 3.871871 mhz isoptimum for achieving close accuracy in the derivation of all the tonesdesired without the undue cost and propagation time difficultiesassociated with higher frequencies.

After the signal from the master oscillator has been divided by thefrequency divider chain 2 to the selected audio tone. the audio tonepasses through a mode selector switch 4 and is impressed on the inputterminals of a plurality of SPST switches 5a, Sb. 5c. 5d. .5 to selectone or more of the voicing circuits 6a. 6b. 6c. 6d. .6" in order toalter the waveform to provide the timbre of a given instrument.

The conditioned tone is then amplified by an amplitier 7 by an amountdetermined by the position of volume control 8 to drive a soundtransducer such as the head phones 9 or speaker 10. Additionally. adecibel meter It is utilized to monitor the intensity of the toneimpressed on the sound transducer in order that the apparatus may beused to test the hearing acuity ofa person across the audio spectrumcontrolled by the tone selector switch 3. In a presently preferredembodiment of the invention. the apparatus covers three chromaticoctaves extending one and one-half octaves on each side of middle C.

It is apparent that the apparatus. as so far described, may be utilizedto generate a very closely controlled tone of a selected frequency whicha trained musician or craftsman can readily use to tune an instrument.However, a prime merit of the apparatus is its versatility including theability to visually compare known and unknown tones for tuning andtraining purposes as will become apparent while the descriptionproceeds.

In order to compare the frequency of an unknown audio signal againstthat of a known standard frequency, it is desirable to integrate thestandard signal for a predetermined number of cycles to arrive at aperiod which can be compared against the period of the unknown signal.This approach permits an expansion of the known and unknown perioddifference in accordance with the precise number of oscillator cyclescomprising a standard period. Referring again to FIG. 1, it will beobserved that the output signal from the crystal oscillator 1 is alsoapplied to period gate logic 12. The output from the period gate logic1! drives a counter and decoder 13 which counts a number of cycles fromthe crystal oscillator l determined by the setting of a period selectorswitch 14. The period selector switch 14, similar to the tone selectorswitch 3, functions to variously interconnect adjacent stages andfeedback among the several stages in the counter chain in the counterand decoder 13 such that an output signal will issue when the counterreaches a predetermined count. As those skilled in the digital arts willappreciate. this can be carried out either with preset countertechniques or straightforward decoding. The presently preferredelectrical embodiment of the period gate logic l2. counter and decoder13, and period selector switch 14 is depicted in FIG. 3. By way ofexample. if the counter and decoder 13 issues an end of period signalafter receiving 440 counts from the crystal oscillator 1., the periodbetween the beginning of the first count and the end of the last countwill be the one-half the period of a standard 440-A. i.e.. approximatelyl/880th of a second.

A tunable audio oscillator 15, under operator control by means of tuningknob 16, is coupled through input selector switch 17 to one of theterminals of the mode selector switch 4. Therefore. if the mode selectorswitch is thrown to its alternative position. the tone generated by theaudio oscillator 15 is passed through the selected voicing circuit foraudible reproduction through the head phones 9 or speaker 10.Additionally. the output from the audio oscillator 15 is coupled to theperiod gate logic l2 and through isolation amplifier 24 to the gatingperiod comparator 18. Preferably the output waveform from the audiooscillator 15 approximates a square wave to properly drive the voicingcircuits and also to accurately institute and stop logical action in theperiod comparator network. The presently preferred electrical embodimentof the isolation amplifer 24 and period comparator 18 is depicted in H0.4.

Assume that an operator is attempting to tune the audio oscillator 15 toan A at 440 Hz. This tuning effort is carried out by setting the toneselector switch 3 to the appropriate position and throwing the modeselector switch 4 back and forth between its alternate positions foraudible comparison of the standard tone and the operator produced tone.When the operator wishes to make a determination of the accuracy withwhich he has tuned the audio oscillator 15, he may institute acomparison cycle. and the leading edge of a cycle from the audiooscillator 15 is utilized to open gates in the period gate logic 12which permit the signal from the crystal oscillator l to pass into thecounter and decoder 13 which commences to count toward 440 as selectedby the period selector switch 14. When the count of 440 is reached, thefeedback loop 19 carries the end of period" signal back to the periodgate logic 12 to inhibit further counting. Simultaneously. the end ofperiod signal is impressed on the period comparator 18 which. atapproximately the same time. senses the trailing edge of the same halfcycle from the audio oscillator 15. According to the accuracy to whichthe audio oscillator 15 has been tuned. the end of period" signal fromthe counter and decoder 13 and the trailing edge of the same half cyclefrom the audio oscillator 15 may arrive simultaneously or the signalfrom the audio oscillator may slightly lead or lag the end of period"signal. if the leading edge of the signal from the audio oscillator l5arrives slightly early. its period is shorter than U440 of a second. andthe audio oscillator is therefore tuned sharp. Similarly, if the signalfrom the oscillator lags the end of period" signal slightly, its periodis longer than l/44O of a second, and the audio oscillator is thereforetuned slightly flat.

Thus, the output signal from the period comparator l8 impressed acrossthe input terminals to a different amplifier will be zero if the periodsare the same and either mutually positive or negative if the unknownfrequency is sharp or flat. Differential amplifier 20 is provided withzero adjust control 21 to initially set the reading on the pitch meter22 to center scale. Thereafter, lack of coincidence between thetermination of the known period and the unknown period will cause eithera sharp or flat reading on the pitch meter 22 with the amount ofdeflection corresponding to the degree to which the periods differ. Ithas been found in training new students that full scale deflectionshould be on the order of 5 percent off pitch although those skilled inthe art will understand that it is a simple matter to vary the gain ofthe differential amplifier 20 or otherwise alter the sensitivity of thedeviation observed on the pitch meter 22.

For tuning instruments with the assistance of the pitch member 22, theinput selector switch 17 may be thrown to its alternate position whichaccepts signals from a squaring circuit and filter network 23 that isdriven from an external input which may be, by way of example, amicrophone or other pickup in communication with a musical instrumentbeing tuned. The squaring circuit and filter network 23 must be ofspecialized design to function properly with harmonic-rich inputs suchas that of musical instruments and the schematic representation of onesatisfactory electrical embodiment is shown in FIG. 5. The output signalfrom the squaring circuit and filter network 23 cooperates with thefrequency comparator section of the apparatus in precisely the samemanner as that already described for the audio oscillator 15.Additionally, it will be apparent that ear tuning of the external inputmay be carried out by operating the mode selector switch 4 between itsalternate positions.

ln carrying out somewhat more advanced ear training, one must becomeadept at recognizing intervals. For example, a common interval is aminor 3rd constituting 3 half tones such as from A to C. in order toutilize the apparatus to test facility in selecting and recognizingintervals, the operator of the audio oscillator 15 may be asked to tunethe oscillator to a C while listen ing to an A through the head phones 9or the speaker 10. Thus, the tone selector switch 3 is set to pass an Athrough the voicing circuits whereas the period selector switch 14 isset to extract the period of a C. The operator selectively throws modeselector switch 4 to its alternative positions while tuning the audiooscillator 15 until he believes he is hearing the corresponding intervalbetween the two tones. A period comparison may then be carried out todetermine whether he has the correct interval and also how accurate hisfrequency selection has been as indicated by the reading observed on thepitch meter 22. it will be apparent that any desired interval, includingoctaves and intervals in excess of octaves may be selected byappropriate adjustment of the tone selector switch 3 and the periodselector switch 14. Similar interval experimentation may be earried oututilizing the external input in conjunction with an operator controlledmusical instrument.

it will also be apparent to those skilled in the art that the modeselector switch 4, depicted as manually operable in FIG. 1, may beautomatically or electronically actuated to facilitate comparison by theoperator and alleviate the operation of mechanically switching by theoperator.

While the principles of the invention have now been made clear in anillustrative embodiment, there will be immediately obvious to thoseskilled in the art many modifications of structure, arrangement.proportions, the elements, materials, and components. used in thepractice of the invention which are particularly adapted for specificenvironments and operating requirements without departing from thoseprinciples.

I claim:

1. Musical teaching and tuning apparatus comprising:

a. a crystal controlled oscillator;

b. a digital frequency divider coupled to the output ofsaid oscillatorfor dividing the frequency thereof;

c. means for selecting the ratio by which said frequency divider dividesthe output signal from said crystal oscillator;

d. a plurality of voicing circuits;

e. means for coupling at least one of said voicing circuits to theoutput of said frequency divider. output terminals of coupled ones ofsaid voicing circuits being common;

f. an amplifier connected to the output from said voicing circuits;

g. means for controlling the gain of said amplifier;

h. an acoustic transducer driven by said amplifer for reproducing anaudio tone derived from said crystal oscillator by said frequencydivider and shaped by at least one of said voicing circuits; a tunableaudio oscillator; and

mode selector switch means for selecting between the output from saidfrequency divider and the output from said tunable audio oscillator asthe input to said voicing circuits.

2. The musical teaching and tuning apparatus of claim I, which furtherincludes:

a. a squaring circuit for accepting an audio frequency input from anexternal source; and

b. an input selector switch for alternatively coupling the output fromsaid squaring circuit and said tunable audio oscillator to said modeselector switch.

3. The musical teaching and tuning apparatus of claim 2, which furtherincludes:

a. a counter decoder circuit for issuing an output signal in response toa predetermined number of input pulses;

b. means for selecting the number of predetermined pulses which causesaid counter and decoder to issue an output pulse;

c. gating means coupling the output signal from said crystal oscillatorto said counter and decoder, said gating means having additional inputscoupled respectively to receive the output signal from said counter anddecoder and to receive the output signal from the audio source selectedby said input selector switch, said gating means being configured suchthat the leading edge of an audio cycle from said audio signal sourcepermits said counter and decoder to commense accumulating pulses fromsaid crystal oscillator and said output signal from said counter anddecoder inhibits further accumulation of said pulses from said crystaloscillator;

d. a period comparator for receiving said output pulses from saidcounter and decoder and for receiving the next succeeding trailing edgeof a cycle from said audio signal source and for issuing a differentialsignal having a magnitude representing the time difference thcrebetweenand a polarity in- 4. The musical teaching and tuning apparatus of claim1, which further includes a decibel meter disposed in parallel with saidacoustical transducer.

dicative of the time sequence in which said period comparator receivessaid signals; and e. a zero center meter driven by said differentialsignal to thereby indicate that the frequency of the

1. Musical teaching and tuning apparatus comprising: a. a crystal controlled oscillator; b. a digital frequency divider coupled to the output of said oscillator for dividing the frequency thereof; c. means for selecting the ratio by which said frequency divider divides the output signal from said crystal oscillator; d. a plurality of voicing circuits; e. means for coupling at least one of said voicing circuits to the output of said frequency divider, output terminals of coupled ones of said voicing circuits being common; f. an amplifier connected to the output from said voicing circuits; g. means for controlling the gain of said amplifier; h. an acoustic transducer driven by said amplifer for reproducing an audio tone derived from said crystal oscillator by said frequency divider and shaped by at least one of said voicing circuits; i. a tunable audio oscillator; and j. mode selector switch means for selecting between the output from said frequency divider and the output from said tunable audio oscillator as the input to said voicing circuits.
 1. Musical teaching and tuning apparatus comprising: a. a crystal controlled oscillator; b. a digital frequency divider coupled to the output of said oscillator for dividing the frequency thereof; c. means for selecting the ratio by which said frequency divider divides the output signal from said crystal oscillator; d. a plurality of voicing circuits; e. means for coupling at least one of said voicing circuits to the output of said frequency divider, output terminals of coupled ones of said voicing circuits being common; f. an amplifier connected to the output from said voicing circuits; g. means for controlling the gain of said amplifier; h. an acoustic transducer driven by said amplifer for reproducing an audio tone derived from said crystal oscillator by said frequency divider and shaped by at least one of said voicing circuits; i. a tunable audio oscillator; and j. mode selector switch means for selecting between the output from said frequency divider and the output from said tunable audio oscillator as the input to said voicing circuits.
 2. The musical teaching and tuning apparatus of claim 1, which further includes: a. a squaring circuit for accepting an audio frequency input from an external source; and b. an input selector switch for alternatively coupling the output from said squaring circuit and said tunable audio oscillator to said mode selector switch.
 3. The musical teaching and tuning apparatus of claim 2, which further includes: a. a counter decoder circuit for issuing an output signal in response to a predetermined number of input pulses; b. means for selecting the number of predetermined pulses which cause said counter and decoder to issue an output pulse; c. gating means coupling the output signal from said crystal oscillator to said counter and decoder, said gating means having additional inputs coupled respectively to receive the output signal from said counter and decoder and to receive the output signal from the audio source selected by said input selector switch, said gating means being configured such that the leading edge of an audio cycle from said audio signal source permits said counter and decoder to commense accumulating pulses from said crystal oscillator and said output signal from said counter and decoder inhibits further accumulation of said pulses from said crystal oscillator; d. a period comparator for receiving said output pulses from said counter and decoder and for receiving the next succeeding trailing edge of a cycle from said audio signal source and for issuing a differential signal having a magnitude representing the time difference therebetween and a polarity indicative of the time sequence in which said period comParator receives said signals; and e. a zero center meter driven by said differential signal to thereby indicate that the frequency of the audio source signal is on pitch, sharp, or flat, according to whether its period is the same, shorter, or longer than the period during which said counter and decoder accumulated pulses from said crystal oscillator, the degree of deflection providing a quantitative indication of pitch deviation. 